An improved carrier smoothing code filter for IGSO satellite and its application in positioning and orbit determination using single-frequency GPS

Abstract When an inclined geo-synchronous orbit satellite receives navigation signals, the long propagation distance and weak signal strength result in larger measurement noise and frequent cycle slips. The carrier smoothing code (CSC) filter improves the positioning and orbit determination (OD) capabilities by combining the high precision of carrier phase data and pseudorange data. This study first analyzes the quality of global positioning system (GPS) data received from the LT4A satellite, comparing its characteristics and delays with those of ground-based measurements. Subsequently, the Hatch filter is enhanced by a new real-time ambiguity estimation method and the Kalman filter calculates prediction values. This results in an improved filter that is well-suited for satellite-based measurements. Finally, the differences in measurement noise, positioning, and OD are compared for data without CSC processing, Hatch filter processing, and Improved filter processing. The results show that the improved filter reduces data noise to 0.23 m, representing an 80.2% decrease compared to the scenario without CSC processing, and suppresses 60.3% of the epochs with positioning errors exceeding about 50 m. The positioning errors processed by the Hatch filter and the Improved filter are about 189.44 m and 161.28 m, respectively, representing a 1.8% and 16.4% reduction compared to the scenario without CSC processing. For 72 h OD arcs, the OD accuracy is superior to that of 30 h arcs. The orbit overlap RMS for the two filters are 22.66 m and 17.96 m, respectively, representing reductions of 5.2% and 24.8% compared to the scenario without CSC processing. These findings demonstrate that the improved filter can better adapt to satellite-based measurements and enhance single-frequency onboard GPS receivers’ positioning and OD accuracy.